1. Field of the Invention
The present invention relates generally to a method of capping particulate materials of the type having an exposed surface which tends to become airborne due to the influence of environmental factors. More specifically, the invention relates to a method for suppressing dust emissions from dust producing bulk materials, particularly during the transit of such materials.
2. Description of the Prior Art
There are a variety of circumstances in which environmental and economic concerns require capping particulate materials, such as dust producing bulk materials, having an exposed surface of particulate material of the type which tends to become airborne due to the influence of various environmental factors including wind and vibration. One example is the transportation of coal by open rail car. Coal cars travelling from the West to deliver low sulfur coal to Eastern utilities frequently lose between 2 to 5% by weight of their load through undesired dust emissions. Such dust emissions are increased by wind erosion and by the vibration of the rail car during transit.
While attempts have been made in the prior art to cap open rail cars containing dust-producing bulk materials, such caps have generally lacked the strength and structural integrity to perform adequately. In other cases, environmentally objectionable substances were utilized. Dust emissions produced by coal and other bulk materials during handling, storage, processing and utilization are undesirable from a variety of standpoints. Dust emissions from certain of these materials can constitute a health and safety hazard. As a result, dust from coal and other bulk materials must be controlled within defined limits, in many cases specified in federal, state or local laws.
In the area of chemical controls for dust emissions, additives are generally applied to an exposed surface of the bulk material in the form of a liquid spray or foam. U.S. Pat. No. 4,836,945, issued Jun. 6, 1989, to Kestner contains a detailed discussion of various prior art chemical controls including the use of water and oil sprays. Included among the prior art materials are aqueous solutions of vinyl esters, latex emulsions, asphalts, waxes and various other polymers. These prior art formulations have tended to be expensive and, in some cases, have included the use of environmentally objectionable components. Also, the teachings of the previously mentioned patents were apparently directed primarily toward stockpiles of such bulk materials, rather than toward the treatment of such materials during transit, as in an open rail car.
U.S. Pat. No. 5,118,219, entitled "Method of Capping Tailings Ponds", issued Jun. 2, 1992, to Daniel D. Walker, Jr. teaches a method for capping tailings ponds of the type which receive fines-containing aqueous effluent from an industrial process. A mineral formulation is prepared by mixing together lime, a pozzolanic component, a sulfate component and water. The mineral formulation is applied to the surface of the fines-containing tailings pond and is allowed to harden to form a surface coating on the tailings pond. The present invention is an improvement upon the previous formulation, specifically directed toward the capping of particulate materials being transported within a container having at least one opening therein which provides an exposed surface of the particulate material of the type which tends to become airborne due to the influence of environmental factors such as wind and vibration. The improved method of the invention has particular application to the transportation of coal and other dust-producing bulk materials such as, e.g., bulk hazardous waste soil being transported to a landfill, fly ash being transported to a waste dump and other particulate containing bulk materials such as iron ore. Particularly because of the effect of vibration upon the bulk material being transported, the requirements and characteristics of the present formulation differ from those described in the previously mentioned Walker patent. One factor of particular importance in the case of bulk transit is the compressive strength of the ultimately set cap.
The present invention has as its object to provide an environmentally acceptable, semipermeable, cementitious, non-hazardous, solid membrane designed to control dust emissions from bulk dust-producing materials.
Another object of the invention is to provide a capping material and method for controlling dust emission from open-air transport vehicles such as railroad cars carrying coal.